1. Field of the Invention
The present invention relates to drive mandrels or shafts that provide for gripping the internal surfaces of sleeves, tubes or cores on which web material may be wound, and yet allow for speed slippage between the shaft and core when web tension exceeds the torque being applied to the shaft. More particularly, the invention relates to means for gripping and independently slipping multiple cores on a common shaft.
2. Description of the Prior Art
Expandable shafts or mandrels are generally constructed with elements on the surface adapted to be extended radially outward by inflation of bladders within the shaft. Shaft designs fall into two general categories, the lug type and slotted rail type. The former contemplates a number of discreet lugs located at different points along the shaft. Customarily there are one or more bladders located within the shaft that are appropriately inflated to cause the lugs to extend radially outward to grip the web sleeve that surrounds the shaft. The slotted type of expandable shaft customarily includes a plurality of equally spaced slots around the circumference of the shaft and elongated pressure elements located within the slots.
Individual bladders located within the shaft slots are inflated to bear against the pressure elements and extend them radially outward for the gripping of a surrounding web sleeve. Helical slots have also been used in expandable core shafts in the past. The amount of pressure in the bladders generally controls the degree of grip or limit of torque that can be applied to the sleeve or core.
A problem unresolved in the art is the mixing of different sleeve lengths on a common shaft, to accommodate different web widths, materials, sheet thickness, and their effect on individual web tensions as the diameters of the different rolls and their different weights and inertia's change during the run.
U.S. Pat. Nos. 5,445,342; 4,135,677; 4,114,909; 4,026,488; 5,372,331; and 5,379,964; may provide further useful context for the introduction of the present invention.